Patent GB-728859-A (GB)
Title: Improvements in or relating to telecommunication code selection circuits
IPC: H04M1/515
Filed: 1953-02-05
Abstract: 728,859. Automatic exchange systems. SIEMENS & HALSKE AKT.-GES. Feb. 5, 1953 [Feb. 13, 1952; April 19, 1952], No. 3332/53. Class 40 (4). Each wire of a subscriber's line is connected at an exchange to an earthed A.C. supply through separate pairs of signal relays which are oppositely polarized by rectifiers, and the transmission of numerical or other signals whereby coded response of the signal relays is obtained is effected by temporary application of various combinations of direct earth and earth through half-wave rectifiers to one or both of the line wires. A keysender is employed for signalling, and additional keys may be provided which are each allotted to a frequently wanted multidigit number. General arrangement, Fig. 1. The subscriber's line is initially connected to a battery supply bridge SB at the exchange and relays S and SH pull up when the line is looped at hu. Each time a key T1-T11 is operated in the keysender, the line loop is broken at contact 4 and one of the line wires aa, ab is earthed. This earth may also arise from a momentary closure of contact 12, but this feature is entirely optional. One winding of a differential relay X is then consequently short-circuited, either directly or by the release of S, and the relay pulls up and transfers the line to a signalreceiving bridge WB. Relay SH falls back slowly when S is released. Each time an operated key is released the circuit is restored to its initial condition. In a modification, Fig. 2 (not shown), the differential relay is omitted from the line circuit and separate S relays are connected to each line wire. Signal transmission. According to the signalling key operated, earth is applied to one or both of the line wires either directly or through halfwave rectifiers G1-G4, and a circuit is thus completed for an earthed A.C. supply WQ at the exchange through one or more signal relays A-D, each relay being polarized by a rectifier G11-G14. Fifteen possible signalling combinations are available of which eleven are used in the embodiment shown in Fig. 1. The keys T1-T10 are employed for digit transmission, while the key T11 is used for special signals. Proper depression of a key may be indicated by a lamp KL, the short-circuit shown at V being removed. Signal reception. The coded response of the signal relays A-D each time a key is depressed is repeated by corresponding relays A1-D1 which, during the release time of SH, connect potential over a contact tree to an appropriate register lead K1-K11. When relay SH falls back the differential relay X remains held over winding III until the line loop is restored by release of the operated key. The circuit then reverts to its initial condition with the line connected to SB. Further signals are then received in like manner. In a modified exchange circuit, Fig. 3 (not shown), the control functions of the differential relay X are carried out by a slave relay. Transmission of frequently wanted numbers. The substation is equipped with keys Tn1-Tn20 for this purpose in addition to the digit keys T1-T10. In the embodiments shown in Figs. 4 and 5, single contacts of the digit keys are used for signal selection and the line wires are therefore electrically isolated from each other by the use of relays A1-D1. A common selector W is used in the Fig. 4 arrangement which earths its outlets 1-11 in turn, these outlets being connected to appropriate leads ka1-ka10 whereby the successive depression of digit keys is simulated when a relay R1-R20 is operated by a key Tn1-Tn20. When a digit key T1-T10 is used, an auxiliary contact 10 pulls up slow-operating relay U which connects the line wires to the signalling circuit. A lead ka1-ka10 is earthed by the operated key, and if the signalling code pertaining thereto uses one line wire only, a direct connection or a connection through a rectifier G1, G2, G4, G6 is available. Special arrangements involving the relays A1-D1 are employed when the digit keys T5, T7, T9, T10 are used, since the appropriate signalling codes involve the use of both line wires. If any of these keys are depressed, an alternating current circuit over one line wire is completed through a rectifier G5, G7, G9 or G10 and a relay A1-D1 pulls up. A holding winding -and a shunt rectifier G5<1>, G7<1>, G9<1>, G10<1> is then connected to the other line wire. As a result, the signalling circuit is established with one line wire earthed through a rectifier over the operating winding of a relay A1-D1 and the other line wire directly earthed over the holding winding. Each time a key is released relay U falls back and the line loop is reconnected. When a key Tn1-Tn20 is operated, a relay R1-R20 pulls up in series with U and the selector magnet DW is energized over an off-normal contact kwo. The selector moves to outlet 1 and connects earth to a lead ka1-ka10 as previously described so that the first signal is transmitted. Relay U is then disabled by an opened magnet contact 51dw and falls back slowly due to the charging current of a condenser ko. When this relay is back the line loop is restored and the condenser discharges. DW is also disabled and closes contact 51dw. Relay U and magnet DW then re-operate in turn and the switch moves to outlet 2. The switch continues to step under the control of relay U until it moves to its home position. A lamp UL indicating the operations of U may be provided. Alternative arrangement, Fig. 5. No local source of current is used; a separate selector W1-W20 is also provided for each key Tn1-Tn20. When the line is taken into use, relay H pulls up in the loop circuit. Depression of a digit key T1-T10 opens a contact 104 so that the line loop is interrupted and relay H falls back. The signalling circuit is then connected to the line wires and signal transmission is effected as previously described. If connection to a frequently wanted subscriber is required, a key Tn1-Tn20 is operated which closes contact 106 and earths'wire aa until H falls back. At the exchange the line wires are transferred from the battery feed supply bridge SB to the signal receiving bridge WB. Before the transfer takes place, battery over wire aa energizes the drive magnet DW1-DW20 of the selector corresponding to the operated key and the switch is stepped to outlet 1. Assuming that key Tn1 is used, the energized magnet Dw1 opens contact 3dw1 so that a self-disabling relay Ul pulls up and then falls back slowly. During the release time of U1, earth at contact 125u1 is applied over selector outlet 1 to an appropriate lead ka1-ka10 and the first signal is transmitted as previously described. When U1 releases this earth is removed, and the battery supply bridge is again connected to the line wires at the exchange and pulls up magnet Dw1. The selector steps to outlet 2 and the cycle of operations is repeated, the signal transmitted being determined by the lead ka1-ka10. which is connected to the outlet. The selector outlets are unwired when signal transmission is not required. When the selector reaches its home position a wiper 130 disables the operating circuit of relay U1 and the switch is stopped. Modified versions of Figs. 4 and 5. The line isolating relays A1-D1 in the signalling circuit are not used. Only those portions of the circuits affected by the modifications are shown in Figs. 6 and 7 which correspond to Figs. 4 and 5 respectively. A separate ka lead is provided for each earth connection to a single line wire and the digit keys T5, T7, T9, T10 which involve signal transmission over two wires thus require double contacts. Simultaneous earthing of two ka leads is also required when the digits 5, 7, 9 and 10 of a frequently wanted number are automatically transmitted. In the arrangement shown in Fig. 6, certain of the selector outlets are connected to two ka leads over contacts of an operated relay R which determines the digits to be signalled. In Fig. 7, each selector has an auxiliary wiper W1<1> which enables earth to be applied simultaneously where necessary to two of the ka leads.